This was once a mysterious phenomenon that was called "sea fire" or "sea twinkle" by sailors and coastal dwellers. It is the transformation of
chemical energy into
light energy by a living being which then emits this light. Bioluminescence differs from
fluorescence and
phosphorescence because the latter two require contact with light to trigger the phenomenon.
N. scintillans produces luminous flashes, which constitute bioluminescence, during mechanical stress. This phenomenon can therefore be observed in agitated water, i.e. when boats are passing, near the coast at wave level or after water agitation.
Luciferin combines with
luciferase and the two react with oxygen to form an oxidized complex. The luciferin then emits a
photon. Of course, the reaction itself is not so simple, in fireflies it also requires two additional cofactors,
ATP and
magnesium. There are also several types of luciferin and each is associated with a specific luciferase giving different chemical reaction systems. The light is produced by mechanical stimulation due to
shear stress. The deformation of the cell membrane causes an
action potential across the
vacuole membrane caused by
Ca2+ ions released from intracellular stores. And is involved in the activation of GTP-binding protein coupled receptors in the plasma membrane. Most of the
Ca2+ ions are released from intracellular stores, while some are released from extracellular sources. Under mechanical disturbance, this action potential releases an influx of
protons from the acidic vacuole to the scintilla, lowering the
pH from 8 to 6. This changes the conformation of luciferase making it active. Luciferin contains a
binding protein that prevents it from auto-oxidizing in an alkaline pH. It releases it by a conformational change in acidic pH, activating luciferin. This
activation then allows the enzyme to oxidize luciferin to oxyluciferin. It is this molecule that leads to the emission of photons by an unknown process. The dinoflagellate luciferase gene (lcf) of
Gonyaulacales are currently the focus of scientists' research, while the bioluminescent gene sequences of
Noctiluca scintillans do not belong to the
Gonyaulacales order, so
Noctiluca scintillans is the first representative of heterotrophic dinoflagellates, which helps to understand the extreme diversity of low-carbon fluoride compounds in dinoflagellates. In
Noctiluca scintillans, the dinoflagellate luciferase gene (lcf) is highly simplified compared to photosynthetic dinoflagellates. It consists of only a single domain that is shorter than those found in photosynthetic species and exists as a hybrid gene fused with the luciferin-binding protein (lbp). This contrasts with photosynthetic dinoflagellates, which typically have lcf genes composed of three tandemly repeated domains. The structural simplification in
Noctiluca scintillans includes a shorter N-terminal region and the absence of three out of four histidine residues believed to be involved in pH regulation, although functional pH sensitivity is retained.
Noctiluca scintillans is one of the most common bioluminescent organisms in coastal areas of the world, its bioluminescence lasts 80 ms. In areas where it is abundant, its bioluminescence acts as a sensitive expressive character and provides an indication of its spatial distribution. There is a large variability in the duration of bioluminescence between species that is not yet explained. But it may be related to the number of scintillations present, the volume of scintillations, the amount of luciferin available and the amount of scintillations stimulated by proton influx which can approach 5% for
Noctiluca scintillans. Some other phenomena influence the intensity of bioluminescence and even its presence. First of all, it has been found that it varies with the
circadian rhythm. The molecules are destroyed at dawn and start to be resynthesized at dusk. Their concentration is highest during 4 hours of the night, when it reaches 10 times the daytime concentration. The intensity of the emitted light is influenced by the
physiological status of the cell and also by environmental factors. The intensity is also influenced by the amount of light received during the previous day. This last phenomenon is due to the fact that for species containing
chlorophyll (such as the green genus for
Noctiluca scintillans), the mechanism of bioluminescence is a little different and depends on the
chlorophyll a molecule. Bioluminescence is therefore influenced by cell sensitivity to stimulation, specific response, time, physiology and environmental factors.
N. scintillans is less prone to predation when in this 'phase' of bioluminescence, so this may be one of the functions of bioluminescence. The function of bioluminescence has not yet been proven, it is only a theoretical concept. However, it seems to act as a defence against predators, for oxygen, camouflage and seduction.
N. scintillans is not the only species capable of bioluminescence;
Pyrocystis lunula, a dinobiont, or certain bacteria are also capable of it. ==Risks==